4.2 Photovoltaic Generator Technology 4.2.1 European Solar Array Subsystems Preliminary development of a high power solar array (10 to 30 kilowatts) for COLUMBUS has been successfully carried out under the Columbus Preparatory Supporting Technology Programme. The use of bifacial solar cell configurations is quite attractive for applications in the second generation of the COLUMBUS program, as well as in future telecommunications applications. It is possible that an appropriately directed technology programme will be initiated on the subsystem level based on existing development efforts at the component level. A preliminary assessment at the systems level of concentrator solar arrays for use on deep space missions and in LEO has recently been conducted. Preliminary development of critical components and sub-assemblies is currently underway at ERNO-MBB in order to gain more detailed information which can provide a sound basis for a more detailed assessment. ESA supports and coordinates national array development programmes. The advanced rigid array and a retractable version thereof are being developed at Fokker, an upgraded version of the Generateur Solaire Rigide is being developed by Aerospatiale, and the mark 3 rigid panel array is being developed by MBB. 4.2.2 Assembly Development Activities ECS/MARECS and various recent non-ESA satellites have experienced significant unexpected power loss problems on orbit. There have been two responses to this - first, an investigation of the interaction of solar arrays and the space environment, and second, the development of improved design concepts. A general investigation of the interactions of high voltage (50 to 200 volts) solar arrays with the space environment is under way. Design improvements such as blanket integrated blocking diodes are integrated in this activity. The effects of plasma, ultraviolet radiation, thermal cycling, micrometeoroids, and atomic oxygen are being covered in this study. The groundwork for an on orbit experiment to investigate solar array interactions with the space plasma has been laid at PTS. A flight experiment, possibly in cooperation with NASA, is envisaged. Cover glasses can become electrostatically charged. Electrical short circuits can occur between the active solar cell network and the conductive carbon fiber face sheets (forming the rigid panels) under them. These events have been identified as major risk factors which can lead to power loss at unpredictable times in orbit. ESA plans to develop a rigid panel technology with improved resistance to discharges and solar cell to substrate short circuits. This development activity will proceed along two lines. First, a semiconductive cover glass will be developed to avoid static charging during geomagnetic storms. Second, an insulating rigid panel structure will be developed, where the current carbon fibers are either replaced (e.g.
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